Lawn Fungus Identification and Treatment

One common question we are frequently asked is why home lawns which look healthy in early spring often become brown and pockmarked by midsummer. There are many reasons for the drastic change: close mowing, lack of plant food, insufficient water, soil compaction, insect infestation, and excessively high temperatures which throw certain grasses into dormancy.

But many lawns turn brown in the absence of any of these factors. The type of browning I have in mind occurs primarily during and after periods of excessive rainfall, or when lawns are watered frequently during dry spells with the hose or with sprinklers.

During the last few years I have personally examined numerous unhealthy lawns as well as many clods of browned turf from lawns which had received what is usually considered excellent care. I found that the most common cause of browning was due to infection by one or more kinds of fungi, and not to the hot, blistering sun or other agents as most of the home owners suspected.

A great deal has been written about lawn diseases. Most of this information, however, was based on observations of turf on golf courses, particularly on the greens. The fungus diseases known as brown patch, dollar spot and copper spot are rather common on golf greens because the turf in such areas consists mainly of bent grasses. Bents are not only more susceptible to these diseases but also to insect pests such as chinch bugs and Japanese beetle grubs. Golf greens are watered almost daily during dry spells, a practice which promotes development of many fungus diseases.

Golf Courses Get Fungus Too!

The fungi which attack grass varieties in most home lawns, however, are not the same as those in golf greens. A few home lawns contain a good percentage of bent grasses but these are the exception. The fungi in the average home lawn do not succumb to the same chemicals that have been used successfully for many years to control fungi on golf courses.

Home lawns containing bluegrass and fescues are subject to one or more fungus diseases known by the peculiar names “going-out,” “melting-out” and “fading-out.” The fungi known as helminthosporium and curvularia, which have become prevalent in home lawns in the Eastern United States, are responsible for these diseases. I suspect they are also present in other parts of the country where bluegrasses and fescues are used but that they are diagnosed as dollar spot or one of the other diseases common to golf greens.

All three of the “out” diseases start as small, more or less circular, dead spots scattered here and there in the lawn. Although they get started relatively early in the growing season, they are frequently overlooked because most of the lawn is still lush and vigorous. With heavy rains, or frequent sprinkling (especially late in the evening), the spots enlarge and coalesce until most of the lawn turns brown by midsummer.

The “out” diseases attack lawns at different times during the growing season. In the Northeast, for example, Kentucky bluegrass may be attacked by the “going-out” disease at any time from mid-April to late May. Some varieties of bluegrass, by the way, appears to be resistant to the disease. The “melting-out” disease may strike Kentucky bluegrass, fescues and even bent grasses, between early spring and the arrival of hot weather. The “fading-out” disease attacks nearly all species of grasses after the advent of hot weather.

By using the time of disease appearance as a guide, therefore, the homeowner can sometimes pinpoint the disease involved. As with so many diseases of both plants and animals, however, positive diagnosis can be made only by an expert. With information on spore size and shape, and with the aid of a microscope, he can quickly determine which fungus is causing the trouble. Spores of the causal fungus are usually present in large numbers on diseased blades of grass.

This is hardly the place to describe the difference between fungi which cause grass diseases. Suffice to say that the “melting-out” and the “going-out” diseases are caused by helminthosporium fungi whose spores are cigar shaped and are divided into five to ten more or less equal cells. The curvularia fungus which causes “fading-out” has spores that are bent or curved and are divided into three to five cells of unequal diameter. The fungi which cause brown patch, dollar spot and other diseases of golf greens also have definite characteristics which are entirely different from those which cause the “out” diseases.

You may wonder why I take the time and space to mention these differences. The reason is that I want to stress the importance of knowing what disease or fungus is involved at the very start so that the correct control material can be selected. Some materials will control one disease and not another. This explains why some gardeners fail to achieve good disease control.

Chemical Fungus Control - One Size Fits All?

If a single chemical capable of controlling all fungus diseases of turf were available, there would be no need for a specific diagnosis. Until one becomes generally available, therefore, it would pay to get a positive diagnosis from a state plant pathologist or other expert. Chemicals are available for preventing the “out” diseases. These, as well as “melting-out,” can be controlled.

The time to start lawn treatments with any control material is early in the growing season, well in advance of any disease outbreak. By applying a fungicide as soon as a few brown spots appear in the lawn and reapplying it every 10 days to 2 weeks for 3 or 4 times, the harmful fungi cannot gain a strong foothold in the lawn. In fact, with adequate applications of the proper fungicide, the fungus population will be kept so low that lawns can be watered more frequently during dry spells with little danger of an outbreak of disease. It is needless to add, perhaps, that the chemical should be applied uniformly and exactly as directed. Applying more than directed for a given area may damage the desirable grasses, and applying less than the recommended dosage may fail to give control.

Scientists have developed so-called “shot-gun,” or “broadspectrum” fungicides for turf which will control most of the fungus diseases to which lawns are subject. The material sold under the trade name Kromad prevents and controls brown patch, dollar spot, copper spot, and pink patch, as well as the “out” diseases caused by helminthosporium and curvularia.

In the final analysis, success in combating diseases of lawns depends on keeping the growing balance in favor of the desirable grasses at the expense of the fungus parasites. By making periodic applications of the proper fungicide we keep down the fungus population and help the grass grow.

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